Physicians as a group are trained to have excellent clinical skills, but the difference between an average and extremely successful physician often comes down to factors outside of their ability to provide clinical care. 

Human NK cells express multiple receptors that interact with HLA class I molecules which, in turn, suppy peptides that bind HLA-E to form CD94/NKG2A NK receptor ligands. These peptides correspond to -22 to -14 residues in the leader sequences of HLA-A, HLA-B and HLA-C binding to the HLA-E site. Methionine – 21 delivers functional peptides in stark contrast to threonine – 21 which does not.